14 - Technologies for global telecommunications using undersea cables

Abstract

This chapter gives an overview of the specificities of submarine links with respect to terrestrial links and provides a few examples of recently deployed undersea systems. Today's channels are modulated at a 10 Gbit/s rate, but the deployment of systems based on the next-generation standard bit rate, namely, 40 Gbit/s, has already begun in terrestrial networks. However, the migration to 40 Gbit/s in these networks can be quite challenging. Over the longest transoceanic distances, it will likely require a thorough redesign of the system, involving higher-performance repeaters and new fiber cables. Substituting older 10 Gbit/s or older 2.5 Gbit/s terminals by 10 Gbit/s terminals equipped with the latest technological advances has already proved very effective for extracting more capacity out of existing cables. This chapter also addresses the challenges associated with both green-field deployments and system upgrades. Original fiber arrangements, alternative modulation formats, alternative detection schemes, new amplifiers, and advanced forward-error correction (FEC) are all potential enablers for making submarine links compatible with a 40 Gbit/s channel rate. While the maturation of 10 Gbit/s technologies has opened remarkable opportunities to extract more capacity out of already laid cables, the research efforts on 40 Gbit/s technologies detailed in this study serve as ground for the development of next-generation systems. The key technologies are related to fiber selection and arrangement, to amplifier design, to modulation formats, to detection techniques, and to advanced impairment-mitigation solutions.